> Is it possible to parse implicit operators, like the regular> expression concatenation operator, with a recursive descent parser?

Yes, you can do it mostly by standard grammar-rewriting techniques.

Let us take regular expressions as an example. We start with the
grammar:

R -> R | R
R -> R R
R -> R *
R -> a

Note that the | above is a terminal. a stands for any alphabet symbol.

We start by eliminating ambiguity. We choose (as normal) | to bind
weaker than concatenation which binds weaker than Kleene-star. We
also choose | and concatenation to be right-associative. They are
semantically fully associative, so we could choose any. But we get
less left-recursion to eliminate later by choosing them to be
right-assciative.